In mammals, they found a mechanism for the formation of males without a Y chromosome

A team of researchers led by Professor Asato Kuroiwa from Hokkaido University determined how

sexual differentiation occurs in Amami rats, a species of mammal that does not haveThe Y chromosome and the Sry gene located on it, which is responsible for the formation of males.

The prickly rat Amami is an endangered rodent,found only on the island of Amami-Oshima in Japan. It is one of four known mammals that lack a Y chromosome. However, adult rats are divided into two traditional species - male and female, whose physiology is different.

Researchers collected tissue samples from three malesand three female Amami spiny rats and used them to create genome sequences for each individual. Comparative analysis revealed a duplication (doubling) of the DNA sequence, which was present only in males. This duplicated region was located upstream of the Sox9 gene on the third chromosome.

Duplicate Enh14 region on chromosome 3 in male Amami mice. Image: Miho Terao et al. Proceedings of the National Academy of Sciences

This gene in other mammals isis a target for Sry, is well studied and is responsible for the differentiation of the testes. The scientists found that doubling the DNA sequence activates the Sox9 gene in the absence of Sry. To confirm their hypothesis, the scientists injected the duplicated sequence into female mouse embryos. This change led to the formation of testicles in animals, and not ovaries.

This is the first discovery of the mechanism that controlssexual dimorphism in mammals without a Y chromosome. Researchers will continue to work to understand if a similar mechanism works in other species that lack a Y chromosome, and if there are other similar factors.

In mammals, including humans, the differencebetween male and female at the chromosomal level is due to the X- and Y-chromosomes. Generally, females have two X chromosomes (XX), while males have an X and a Y chromosome (XY). The Sry gene on the Y chromosome triggers testicular formation.

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On the cover: Amami Mouse. Image: Asato Kuroiwa, Hokkaido University